1. Field of the Invention
The present invention relates to computer networks and to interface devices for connecting host computers to networks. More particularly, the present invention relates to power management in high speed network interface devices supporting multiple link speeds.
2. Description of Related Art
Computer systems often include network interfaces that support high speed data transfers between a host computer and a data network. Such computer systems include an adapter such as a Network Interface Card, (NIC), or a chip for the network interface on the motherboard. Such adapters typically connect to a host processor via a bus.
Many computer systems include power management logic which puts the system to sleep, or in a lower power mode, in response to activity in the system. When the system is asleep, for example, the operating system (OS) ceases operation. To bring the system awake, the operating system must be reloaded, such as through a boot sequence. When the operating system is inactive, the power consumed by the system is reduced. Such systems can be said to have an OS-present state, and an OS-absent state. Protocols have been developed by which remote management systems can wake up a system in an OS-absent state, by sending special wake up packets which the network interface is adapted to recognize without host assistance.
In the last few years, host adapters that communicate with any type of network medium have been required to operate in a variety of power managed modes. The basic idea of a power-managed system consists of the following: when a host is not in use, it can be allowed to go into a lower power-state which allows for significant power savings. This is preferable to a complete shutdown, which requires a lengthy boot-up process to allow work to continue. In lower power states, a host monitors certain possible events that would cause it to ‘wake-up.’ These events could be a keystroke, movement of the mouse, phone ring, or a signal from a local area network (LAN). In the case of Ethernet networking, certain packets can be enabled to wake-up a host computer at any point within the network. This is a very useful feature since it allows network administrators the ability to maintain and upgrade systems from a remote location during non-working hours. It is possible for software to manage the power states of an adapter in order to ensure compliance with power consumption specifications, but there are many times when software becomes unavailable (Common operating system OS crashes in Microsoft Windows systems, power outages, and user intervention).
Since wake-up devices need to remain operational in order to monitor wake-up events, they are allocated power in order to perform their function. However, specifications for standard bus systems, such as the PCI 2.2 Bus Specification and the InfiniBand 1.0 Specification, place strict power requirements on wake-up devices. Unfortunately a Gigabit Ethernet adapter cannot operate at Gigabit speeds and comply with these power requirements using available technologies. In the case of the PCI 2.2 specification this power allotment is 1.2 watts, and for InfiniBand it is 1.3 watts. In both these cases it is impossible with today's technology to maintain a Gigabit Ethernet link and consume less than 1.2 watts. Cutting edge technology seems to suggest that we may see a Gigabit physical layer (PHY) chip consuming a little less than 1.0 watt in the next few years, but a Gigabit PHY is only part of the power consumption needed for a wake-up apparatus to work at Gigabit speeds. Many experts would argue that we will never see a Gigabit adapter consuming less than 1.2 watts. However, not being able to maintain a Gigabit link in a power-managed adapter in a lower power mode has not been an important issue since a high speed networking connection is not necessary to receive a wake-up packet. When the host is ‘asleep’ it is only necessary that it is able to receive a packet—how fast it gets there is of no importance, therefore Gigabit adapters can negotiate to slower speeds before going to sleep.
At the present time, software manages the power states of adapters. When a host plans to go to sleep, host software negotiates to slower networking speeds to save power. However, there can be times when a host attempts to be in a sleep-mode when software intervention is impossible. This can occur when the OS is inoperative or after power is restored following a power-loss. 10/100 Ethernet adapters can be in a fully operational state and still consume less than 1.2 watts whether operating in the 10 M bit or 100 M bit mode. So, the fact that software is not always available to manage power-states of 10/100 Ethernet adapters is not an issue. Since a Gigabit Ethernet adapter cannot be run within the specified power in the sleep mode, a new method or apparatus is needed to power manage the adapter in the absence of software control.
Accordingly, is desirable to provide a solution to this power management problem associated with high speed communication protocols that consume greater power than specified for the host systems in lower power modes, that is operable when the host software does not have access to the network interface or is not operating.